Answer:
1. An echo can be heard only if the person is in the range of both the sound waves coming directly from the source and the reflected waves and at a distance of more than 16.6 meters in front of the reflecting source.
A person behind the reflecting source will likely not hear an echo. If the interval of time between the instant a sound wave reaches the ear and the instant the reflected wave reaches the ear is less than 0.1 second, the person can’t hear the echo separately from the original sound. Finally, the person can’t be too close to the reflecting surface.
2. Clay tile would be the least efficient because it has the lowest coefficient of absorption (3%). This means that the energy remaining in a reflected wave is 97%, which is very high. (Remember that this is equal to 100 minus the coefficient of absorption). Very little of the sound energy would be absorbed.
3. Infrasonic and ultrasonic vibrations can’t be heard by humans because they’re outside of the range of frequencies that can be detected. Infrasonic vibrations have a lower frequency than can be heard by the human ear; ultrasonic vibrations have a higher frequency than can be heard by the human ear. Infrasonic vibrations can be felt if the amplitude is great enough. Ultrasonic vibrations are utilized in sonar equipment and in applications to detect flaws in steel castings and to remove grease or foreign material from machine-part surfaces.
4. If the sound comes from the right side, the waves reach the right ear before the left ear. If the sound comes from the left side, the waves reach the left ear before the right ear. The difference between the phases of waves reaching both ears is detected by the ears and then interpreted by the brain. If the sound comes from directly above, directly below, directly ahead, or directly behind, the sound waves reach both ears in phase and is interpreted as such by the brain.
Explanation:
